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Multiperiodic Pulsations in the Be Stars NW Ser and V1446 Aqlhttp://publi2-as.oma.be/record/2648
We present accurate differential photometry of two Be stars: NW Ser and V1446 Aql. Both stars show rapid variations in amplitude, probably due to a beating phenomenon. Two additional significant frequencies are also detected in both stars. This would be the first unambiguous ground-based detection of photometric multiperiodicity in Be stars which may constitute a proof of the presence of non-radial pulsations (nrp) as the origin of the short- term variability. Further observations are planned in order to confirm the detected frequencies. Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:17:08 GMThttp://publi2-as.oma.be/record/26482006Multiperiodic Pulsations in the Be Stars NWSer and V1446Aqlhttp://publi2-as.oma.be/record/2626
We present accurate differential photometry of two Be stars: NWSer and V1446Aql. Both stars show rapid variations in amplitude, probably due to a beating phenomenon. The spectral analysis confirms the presence of two close frequencies. A preliminary instability analysis indicates that l=2 or l=3 g modes are predicted unstable for both stars. In addition, NWSer could be one of the very few ß Cephei and SPB hybrid star. This would be the first unambiguous ground-based detection of photometric multiperiodicity in Be stars which may constitute a proof of the presence of non-radial pulsations (nrp) as the origin of the short-term variability. Further spectroscopic and photometric observations are planned in order to confirm the detected frequencies. Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:17:08 GMThttp://publi2-as.oma.be/record/26262007First results on Be stars with CoRoThttp://publi2-as.oma.be/record/2556
In this paper we present an overview of the analysis of some of the Be stars observed with the CoRoT satellite up to this date. Be stars are very fast-rotating B-type stars which may pulsate as ß Cephei or SPB stars. CoRoT has already observed 5 bright Be stars in the seismology fields and several tens of fainter ones in the exoplanet fields with an unprecedented quality and with a time duration from 20 to 150 days. Multiple frequencies are detected in the majority of the stars. Pulsations, outbursts, beating phenomenon, rotation, amplitude variability, etc. have been found in their light curves. In order to complement this study, ground-based spectroscopic data have also been analysed for the stars located in the seismology fields. Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:17:07 GMThttp://publi2-as.oma.be/record/25562008Low-amplitude variations detected by CoRoT in the late type Be star HD 175869http://publi2-as.oma.be/record/2325
We present the analysis of the CoRoT data of the B8IIIe star HD 175869 observed during a short run (27.3 days). The light curve shows low-amplitude variations of the order of 0.3 mmag. A frequency within the range determined for the rotational frequency and its 5 harmonics are detected. Other significant frequencies with a low amplitude of a few ppm are also found. The analysis of line profiles from ground-based spectroscopic data does not show any variation. Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23252009Preliminary results on the pulsations of Be stars with CoRoThttp://publi2-as.oma.be/record/2323
We present preliminary results of the study of pulsations of Be stars from CoRoT observations. CoRoT detected many pulsation frequencies in all observed Be stars, usually interpreted in terms of g-modes but sometimes also corresponding to p-modes. Even in late Be stars, for which the detection of pulsation frequencies is very difficult from the ground, because of their very low amplitude, the quality and precision of the CoRoT data allows us to detect many frequencies. Seismic models have not yet been calculated but the calculations are ongoing. Neiner, C.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23232009The B0.5IVe CoRoT target HD 49330. I. Photometric analysis from CoRoT datahttp://publi2-as.oma.be/record/2312
Context: Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection. Aims: We analyze the pulsational behavior of the early B0.5IVe star HD 49330 observed during the first CoRoT long run towards the Galactical anticenter (LRA1). This Be star is located close to the lower edge of the ß Cephei instability strip in the HR diagram and showed a 0.03 mag outburst during the CoRoT observations. It is thus an ideal case for testing the aforementioned hypothesis. Methods: We analyze the CoRoT light curve of HD 49330 using Fourier methods and non-linear least square fitting. Results: In this star, we find pulsation modes typical of ß Cep stars (p modes) and SPB stars (g modes) with amplitude variations along the run directly correlated with the outburst. These results provide new clues about the origin of the Be phenomenon as well as strong constraints on the seismic modelling of Be stars. Tables 3 to 7 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/506/95 Huat, A.-L.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23122009The B0.5 IVe CoRoT target HD 49330. II. Spectroscopic ground-based observationshttp://publi2-as.oma.be/record/2311
Context: We present spectroscopic ground-based observations of the early Be star HD 49330 obtained simultaneously with the CoRoT-LRA1 run just before the burst observed in the CoRoT data. Aims: Ground-based spectroscopic observations of the early Be star HD 49330 obtained during the precursor phase and just before the start of an outburst allow us to disantangle stellar and circumstellar contributions and identify modes of stellar pulsations in this rapidly rotating star. Methods: Time series analysis (TSA) is performed on photospheric line profiles of He I and Si III by means of the least squares method. Results: We find two main frequencies f1 = 11.86 c d-1 and f2 = 16.89 c d-1 which can be associated with high order p-mode pulsations. We also detect a frequency f3 = 1.51 c d-1 which can be associated with a low order g-mode. Moreover we show that the stellar line profile variability changed over the spectroscopic run. These results are in agreement with the results of the CoRoT data analysis, as shown in Huat et al. (2009). Conclusions: Our study of mid- and short-term spectroscopic variability allows the identification of p- and g-modes in HD 49330. It also allows us to display changes in the line profile variability before the start of an outburst. This brings new constraints for the seimic modelling of this star. Based on observations made with ESO Telescopes at La Silla Observatory under the ESO Large Programme: LP178.D-0361, and on data collected with the TBL at Pic du Midi Observatory (France). Floquet, M.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23112009Pulsations in the late-type Be star HD 50 209 detected by CoRoThttp://publi2-as.oma.be/record/2310
Context: The presence of pulsations in late-type Be stars is still a matter of controversy. It constitutes an important issue to establish the relationship between non-radial pulsations and the mass-loss mechanism in Be stars. Aims: To contribute to this discussion, we analyse the photometric time series of the B8IVe star HD 50 209 observed by the CoRoT mission in the seismology field. Methods: We use standard Fourier techniques and linear and non-linear least squares fitting methods to analyse the CoRoT light curve. In addition, we applied detailed modelling of high-resolution spectra to obtain the fundamental physical parameters of the star. Results: We have found four frequencies which correspond to gravity modes with azimuthal order m=0,-1,-2,-3 with the same pulsational frequency in the co-rotating frame. We also found a rotational period with a frequency of 0.679 cd-1 (7.754 µHz). Conclusions: HD 50 209 is a pulsating Be star as expected from its position in the HR diagram, close to the SPB instability strip. Based on observations made with the CoRoT satellite, with FEROS at the 2.2 m telescope of the La Silla Observatory under the ESO Large Programme LP178.D-0361 and with Narval at the Télescope Bernard Lyot of the Pic du Midi Observatory. Current address: Valencian International University (VIU), José Pradas Gallen s/n, 12006 Castellón, Spain. Current address: Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; CEA, IRFU, SAp, centre de Saclay, 91191 Gif-sur-Yvette, France. Diago, P. D.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23102009Low-amplitude variations detected by CoRoT in the B8IIIe star HD 175869http://publi2-as.oma.be/record/2309
Context: The origin of the short-term variability in Be stars remains a matter of controversy. Pulsations and rotational modulation are the components of the favored hypothesis. Aims: We present our analysis of CoRoT data of the B8IIIe star HD 175869 observed during the first short run in the center direction (SRC1). Methods: We review both the instrumental effects visible in the CoRoT light curve and the analysis methods used by the CoRoT Be team. We applied these methods to the CoRoT light curve of the star HD 175869. A search for line-profile variations in the spectroscopic data was also performed. We also searched for a magnetic field, by applying the LSD technique to spectropolarimetric data. Results: The light curve exhibits low-amplitude variations of the order of 300 µmag with a double wave shape. A frequency within the range determined for the rotational frequency and 6 of its harmonics are detected. The main frequency and its first harmonic exhibit amplitude variations of a few days. Other significant frequencies of low-amplitude from 25 to a few µmag are also found. The analysis of line profiles from ground-based spectroscopic data does not detect any variation. In addition, no Zeeman signature was found. Conclusions: Inhomogeneities caused by stellar activity in or just above the photosphere are proposed to produce the photometric variability detected by CoRoT in the Be star HD 175869. The hypothesis that non-radial pulsations are the origin of these variations cannot be excluded. Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23092009The pulsations of the B5IVe star HD 181231 observed with CoRoT and ground-based spectroscopyhttp://publi2-as.oma.be/record/2308
Context: HD 181231 is a B5IVe star, which has been observed with the CoRoT satellite during ~5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry. Aims: By analysing these data, we aim to detect and characterize as many pulsation frequencies as possible, to search for the presence of beating effects possibly at the origin of the Be phenomenon. Our results will also provide a basis for seismic modelling. Methods: The fundamental parameters of the star are determined from spectral fitting and from the study of the circumstellar emission. The CoRoT photometric data and ground-based spectroscopy are analysed using several Fourier techniques: Clean-ng, Pasper, and Tisaft, as well as a time-frequency technique. A search for a magnetic field is performed by applying the LSD technique to the spectropolarimetric data. Results: We find that HD 181231 is a B5IVe star seen with an inclination of ~45 degrees. No magnetic field is detected in its photosphere. We detect at least 10 independent significant frequencies of variations among the 54 detected frequencies, interpreted in terms of non-radial pulsation modes and rotation. Two longer-term variations are also detected: one at ~14 days resulting from a beating effect between the two main frequencies of short-term variations, the other at ~116 days due either to a beating of frequencies or to a zonal pulsation mode. Conclusions: Our analysis of the CoRoT light curve and ground-based spectroscopic data of HD 181231 has led to the determination of the fundamental and pulsational parameters of the star, including beating effects. This will allow a precise seismic modelling of this star. Based on observations obtained with the CoRoT satellite, with FEROS at the 2.2 m télescope of the La Silla Observatory under the ESO Large Programme LP178.D-0361, with Narval at the Télescope Bernard Lyot of the Pic du Midi Observatory, and collected from the BeSS database. Table 5 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/506/143 Neiner, C.Fri, 01 Jul 2016 15:17:03 GMThttp://publi2-as.oma.be/record/23082009Photometric variability of the Be star CoRoT-ID 102761769http://publi2-as.oma.be/record/2278
Context. Classical Be stars are rapid rotators of spectral type late O to early A and luminosity class V-III, which exhibit Balmer emission lines and often a near infrared excess originating in an equatorially concentrated circumstellar envelope, both produced by sporadic mass ejection episodes. The causes of the abnormal mass loss (the so-called Be phenomenon) are as yet unknown. Aims: For the first time, we can now study in detail Be stars outside the Earth's atmosphere with sufficient temporal resolution. We investigate the variability of the Be Star CoRoT-ID 102761769 observed with the CoRoT satellite in the exoplanet field during the initial run. Methods: One low-resolution spectrum of the star was obtained with the INT telescope at the Observatorio del Roque de los Muchachos. A time series analysis was performed using both cleanest and singular spectrum analysis algorithms to the CoRoT light curve. To identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT-ID 102761769 by varying its main physical parameters inside the uncertainties discussed. Results: We found two close frequencies related to the star. They are 2.465 c d-1 (28.5 µHz) and 2.441 c d-1 (28.2 µHz). The precision to which those frequencies were found is 0.018 c d-1 (0.2 µHz). The projected stellar rotation was estimated to be 120 km s-1 from the Fourier transform of spectral lines. If CoRoT-ID 102761769 is a typical Galactic Be star it rotates near the critical velocity. The critical rotation frequency of a typical B5-6 star is about 3.5 c d-1 (40.5 µHz), which implies that the above frequencies are really caused by stellar pulsations rather than star's rotation. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Emilio, M.Fri, 01 Jul 2016 15:17:02 GMThttp://publi2-as.oma.be/record/22782010Stochastic gravito-inertial modes discovered by CoRoT in the hot Be star HD 51452http://publi2-as.oma.be/record/2205
Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of iron-peak elements in the envelope of the star. In the Milky Way, p-modes are observed in stars that are hotter than or equal to the B3 spectral type, while g-modes are observed at the B2 spectral type and cooler. Aims: We observed a B0IVe star, HD 51452, with the high-precision, high-cadence photometric CoRoT satellite and high-resolution, ground-based HARPS and SOPHIE spectrographs to study its pulsations in great detail. We also used the lower resolution spectra available in the BeSS database. Methods: We analyzed the CoRoT and spectroscopic data with several methods: Clean-NG, FreqFind, and a sliding window method. We also analyzed spectral quantities, such as the violet over red (V/R) emission variations, to obtain information about the variation in the circumstellar environment. We calculated a stellar structure model with the ESTER code to test the various interpretation of the results. Results: We detect 189 frequencies of variations in the CoRoT light curve in the range between 0 and 4.5 c d-1. The main frequencies are also recovered in the spectroscopic data. In particular we find that HD 51452 undergoes gravito-inertial modes that are not in the domain of those excited by the κ-mechanism. We propose that these are stochastic modes excited in the convective zones and that at least some of them are a multiplet of r-modes (i.e. subinertial modes mainly driven by the Coriolis acceleration). Stochastically excited gravito-inertial modes had never been observed in any star, and theory predicted that their very low amplitudes would be undetectable even with CoRoT. We suggest that the amplitudes are enhanced in HD 51452 because of the very rapid stellar rotation. In addition, we find that the amplitude variations of these modes are related to the occurrence of minor outbursts. Conclusions: Thanks to CoRoT data, we have detected a new kind of pulsations in HD 51452, which are stochastically excited gravito-inertial modes, probably due to its very rapid rotation. These modes are probably also present in other rapidly rotating hot Be stars. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD, and Science Programs), Germany, and Spain. This work uses observations partly made with the HARPS instrument at the 3.6-m ESO telescope (La Silla, Chile) in the framework of the LP182.D-0356, as well as data obtained with Sophie at OHP and from the BeSS database.Table 3 is available in electronic form at http://www.aanda.orgNeiner, C.Fri, 01 Jul 2016 15:17:01 GMThttp://publi2-as.oma.be/record/22052012Multiperiodic pulsations in the Be stars NW Serpentis and V1446 Aquilaehttp://publi2-as.oma.be/record/1997
Aims:We present accurate photometric time series of two Be stars: NW Ser and V1446 Aql. Both stars were observed at the Observatorio de Sierra Nevada (Granada) in July 2003 with an automatic four-channel Strömgren photometer. We also present a preliminary theoretical study showing that the periodic variations exhibited by these stars can be due to pulsation. Methods: An exhaustive Fourier analysis together with a least-square fitting has been carried out on the time series for all four Strömgren bands. Several independent frequencies and non-periodic trends explain most of the variance. A theoretical non-adiabatic code applied to stellar models for these stars shows that g-modes are unstable. Results: Both stars show rapid variations in amplitude, probably due to a beating phenomenon. Four significant frequencies have been detected for each star. Comparison of the observed amplitude ratios for each pulsational frequency with those calculated from theoretical pulsation codes allows us to estimate the pulsation modes associated with the different detected frequencies. NW Ser seems also to show unstable p-modes and thus could be one of the newly discovered ß Cephei and SPB hybrid stars. Further spectroscopic observations are planned to study the stability of the detected frequencies. Tables A.1 and A.2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/472/565 Gutiérrez-Soto, J.Fri, 01 Jul 2016 15:16:57 GMThttp://publi2-as.oma.be/record/19972007First asteroseismic results from CoRoThttp://publi2-as.oma.be/record/1977
About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. Michel, E.Fri, 01 Jul 2016 15:16:56 GMThttp://publi2-as.oma.be/record/19772008First results on the Be stars observed with the CoRoT satellitehttp://publi2-as.oma.be/record/1976
In this paper we present an overview of the analysis of some of the Be stars observed with the CoRoT satellite up to this date. Be stars are very fast-rotating B-type stars which may pulsate as ß Cephei or SPB stars. CoRoT has already observed 5 bright Be stars in the seismology fields and several tens of fainter ones in the exoplanet fields with an unprecedented quality and with a time duration from 20 to 150 days. Multiple frequencies are detected in the majority of the stars. Pulsations, outbursts, beating phenomenon, possible transient modes, rotation, amplitude variability, etc. have been found in their light curves. In order to complement this study, ground-based spectroscopic data have also been analysed for the stars located in the seismology fields. Gutierrez-Soto, J.Fri, 01 Jul 2016 15:16:56 GMThttp://publi2-as.oma.be/record/19762008The pulsations of the B5IVe star HD181231 revealed by CoRoThttp://publi2-as.oma.be/record/1972
We present the first results of the analysis of the light curve of the B5IVe star HD 181231 obtained during a long run (5 months) of the CoRoT mission. The light curve shows clear pulsations and even beating effects. Several frequencies are detected. Ground-based spec- troscopic data have also been analyzed and help to determine the rotation frequency and identify pulsation modes. Neiner, C.Fri, 01 Jul 2016 15:16:56 GMThttp://publi2-as.oma.be/record/19722008A pulsating star inside η Carinae. I. Light variations, 1992-1994.http://publi2-as.oma.be/record/1879
We present and analyze two seasons of intense photometric monitoring in the Stroemgren uvbyHß system of η Carinae (October 1992-August 1994). The luminous blue variable (LBV) in the core did not show much S Dor activity, i.e. it was in a relatively quiescent stage. This situation was very favourable for studying its optical micro variations. It appears that the central LBV pulsates (presumably in a non-radial mode) like other massive evolved stars, the a Cyg variables. The quasi-period is 58.56d. The linear ephemeris is: JD_max_ = 2448875.0 +58.56 E. Support was found for the existence of the presumed periodicity of 52.4d of the so-called &quot;dimples&quot;, shallow dips in the light curve which only last for a few days. The cause may be the eclipse of a small companion or of a hot spot in an accretion disk. The Hß index became bluer by ~0.07mag during the last 11/2 years and shows an oscillation in anti-phase with the 58.56d pulsation, suggesting that the HII region(s) responsible for the hydrogen line emission has a relatively high luminosity. This is another reason to suppose that a second luminous source, perhaps a luminous disk (with a hot spot), may be present in the η Car system. van Genderen, A. M.Fri, 01 Jul 2016 15:16:54 GMThttp://publi2-as.oma.be/record/18791995